The invention relates to clutches in general, and more particularly to improvements in friction clutches. Still more particularly, the invention relates to improvements in friction clutches of the type known as disc clutches wherein one or more motor- and/or engine-driven first discs can be moved into or from more or less pronounced frictional engagement (including no frictional engagement) with one or more second discs which can transmit torque to one or more driven components, e.g., to the input shaft of a transmission in the power train of a motor vehicle.
A disc clutch can be utilized as a so-called starter clutch in the power train of a motor vehicle, especially in a power train which employs an automatic transmission. A motor vehicle wherein the power train embodies an automatic transmission is disclosed, for example, in German patent application Serial No. 198 00 490. An automatic transmission can be of the type known as a multiple-speed (such as three-, four- or five-speed) transmission or an infinitely (continuously) variable transmission (e.g., the one known as CVT) A power train embodying a starter clutch and a CVT is also disclosed in commonly owned U.S. Pat. No. 5,667,448 granted Sep. 16, 1997 to Oswald FRIEDMANN for xe2x80x9cPOWER TRAINxe2x80x9d.
The disclosure of the commonly owned German priority patent application Serial No. 199 19 343.6-12 filed Apr. 28, 1999 as well as the disclosures of all U.S. and foreign patent applications and/or patents identified in the specification of the present application are incorporated herein by reference.
In many instances, a disc clutch comprises a first set of clutch discs (called friction driving discs) and a second set of clutch discs (often called driven plates) which alternate with the clutch discs of the first set. The means for engaging or disengaging the disc clutch often comprises a so-called apply piston which can be caused to move axially to thus urge the clutch discs of the two sets against each other with a variable force and to thus enable the driving discs to rotate the driven plates without any slip or with a selected slip.
As a rule, the starter disc clutch in the power train of a motor vehicle is operated in two stages. The first stage involves rapid axial displacement of the driving discs through a relatively large distance, e.g., to initiate the transmission of torque to the driven plates or discs. The second stage normally involves precision (minute or small) axial displacements of the driving discs to thus select the desired (optimum) extent of frictional engagement between the neighboring (alternating) driving and driven discs, i.e., to accurately select the magnitude of torque to be transmitted between the prime mover (such as an internal combustion engine) and the driven component(s) (such as the automatic transmission) in the power train of a motor vehicle.
If the output part (such as a camshaft or a crankshaft) of an engine transmits a torque which fluctuates within a certain range, such fluctuations entail corresponding variations of the force which the piston of the clutch engaging/disengaging assembly transmits to the interfitted (shuffled) driving and driven clutch discs. The force acts at right angles to the planes of the clutch discs, and any variations of such force normally entail an axial displacement of the driving and driven clutch discs (or of all but one clutch disc) relative to the two hubs, one for the driving discs and the other for the driven discs. One of the hubs has axially parallel internal splines mating with the external (peripheral) teeth of one of the two packages of clutch discs, and the other hub has axially parallel external splines mating with the internal teeth of the other package of clutch discs. The teeth of the clutch discs are, or should be, slidable along but should not rotate relative to the splines of the respective hubs. One of the hubs rotates with the output part of the en-engine, and the other hub is non-rotatably connected with the input element of the transmission.
Whenever the teeth of a clutch disc move along the neighboring splines of the respective hub, this invariably involves the generation of a certain amount of friction. The friction is not constant because its magnitude is a function of the forces acting in the circumferential direction of the clutch discs (i.e., of the magnitude of transitted torque) as well as of the so-called friction factor at the loci of frictional engagement between the teeth of a clutch disc and the splines of the respective hub.
Under ideal circumstances, any changes of pressure of oil or another pressurizable fluid which is employed to move the clutch engaging/disengaging piston axially should result in corresponding predictable axial displacements of the piston and hence in corresponding predictable changes (modulation) of frictional engagement between the driving and driven clutch discs. It has been ascertained that presently known disc clutches fail to satisfy such exacting requirements, and an important reason for such absence of predictability of the magnitude of transmitted torque is the unpredictability of the extent of frictional engagement between the (internal or external) teeth of the clutch discs on the one hand, and the (external or internal) splines of the respective hubs on the other hand. All the aforementioned second stage of operation of a conventional clutch disc normally involves are hysteresis losses rather than an accurate selection of a desired modulation of the torque being transmited between neighboring driving and driven clutch discs.
Conventional disc clutches exhibit certain additional drawbacks. For example, unpredictable frictional engagement between the teeth of the clutch discs and the splines of the respective hubs entails non-uniform wear upon such parts with the resultant generation of noise, escape of lubricant and/or the need for frequent inspection and replacement of parts.
An object of the present invention is to provide a disc clutch which is constructed and assembled in such a way that it can select the magnitude of transmitted torque with a degree of accuracy much higher than that achievable with presently known disc clutches.
Another object of the invention is to provide a disc clutch wherein the interfitted driving and driven clutch discs invariably respond to any and all desired or required changes in the action of the clutch engaging/disengaging arrangement.
A further object of the invention is to provide novel and improved discs for use in a clutch of the above outlined character.
An additional object of the invention is to provide a power train, particularly a power train for use in a motor vehicle, which embodies one or more disc clutches of the above outlined character.
Still another object of the invention is to provide a novel and improved method of transmitting torque between the internal combustion engine and the transmission (such as an automatic transmission) of a motor vehicle.
A further object of the invention is to provide the disc clutch with novel and improved means for shielding the piston of the clutch engaging/disengaging arrangement from corrosive and/or other undesirable influences of the fluid which is employed to shift the piston in its cylinder in order to change the magnitude of the torque which is to be transmitted by the clutch.
Another object of the invention is to provide a disc clutch wherein the exact magnitude of torque which is being transmitted between the two hubs is less dependent upon the magnitude of friction between the teeth of the clutch discs and the splines of the respective hubs than in heretofore known and utilized disc clutches.
An additional object of the invention is to provide novel and improved means for engaging and disengaging a disc clutch.
Still another object of the instant invention is to provide a disc clutch wherein the coolant for the clutch discs can be put to additional advantageous uses.
A further object of the invention is to provide novel and improved means for shielding the apply piston in the engaging/disengaging arrangement of a disc clutch.
Another object of the invention is to provide a simple, compact and relatively inexpensive disc clutch which exhibits the above-enumerated desirable and advantageous characteristics.
An additional object of the invention is to provide a disc clutch the useful life of which is longer than that of conventional disc clutches and which requires less maintenance work than presently known disc clutches.
Still another object of the invention is to provide a novel and improved starter clutch for use in the power trains of motor vehicles, for example, immediately downstream of the rotary output part of a motor, an engine or a hybrid prime mover.
A further object of the invention is to provide a disc clutch which is more compact than heretofore known disc clutches as seen in the axial and/or radial direction of its constituents including the clutch discs and the hubs for the clutch discs.
One feature of the present invention resides in the provision of a disc clutch which comprises a first hub having external splines and being rotatable about a predetermined axis (e.g., about the common axis of the rotary output part of an engine and the input shaft of a transmission in the power train of a motor vehicle), a second rotary hub which spacedly surrounds and is coaxial with the first hub and has internal splines, first friction generating means including at least one first annular clutch disc having a set of internal teeth which mate with the external splines of the first hub, second friction generating means including at least one second annular clutch disc having a set of external teeth which mate with the internal splines of the second hub, and operating means which is actuatable to engage and disengage the clutch. The operating means includes means for biasing the clutch discs against each other. In accordance with a feature of the invention, the teeth of at least one set of teeth are deformable (in accordance with a presently preferred embodiment, all teeth are resilient, i.e., elastically deformable). The teeth of at least one of the discs are movable (along the respective splines) axially of the corresponding hubs.
If each of the two friction generating means comprises a plurality of clutch discs, the clutch discs of one friction generating means alternate with the clutch discs of the other friction generating means, and all clutch discs (with the possible exception of the outermost disc remotest from a reciprocable piston of the aforementioned biasing means) are movable axially relative to each other and relative to the respective hubs. Though it is possible to operate with a single first clutch disc and a single second clutch disc, the improved disc clutch can employ an entire package of coaxial clutch discs; the plural first discs and the plural second discs of such package alternate as seen in the direction of their common axis.
In accordance with a presently preferred embodiment, the biasing means of the clutch operating means comprises at least one fluid-operated cylinder and piston unit, preferably a unit which operates with a hydraulic fluid.
The teeth of at least one set of teeth are or can be deformable in the direction of the common axis of the hubs and clutch discs.
It is often sufficient if only the internal teeth or only the external teeth are resiliently deformable. The internal teeth of the first clutch disc(s) extend radially inwardly beyond an internal surface of each such disc and mesh with the adjacent external splines of the first hub, and the external teeth of the second disc(s) extend radially outwardly beyond an external surface of each such disc and mate with the adjacent internal splines of the second hub.
The external teeth and/or the internal teeth can be a tight sliding fit between the respective internal and/or external splines. Otherwise stated, the external and/or the internal teeth can be dimensioned and configurated in such a way that they are in wobble-free mesh with the respective pairs of (neighboring) splines.
Each clutch disc has an annular main section from which the teeth extend radially outwardly or radially inwardly. The teeth can be of one piece with the respective annular sections, and the thickness of the teeth (as seen in the axial direction of the disc clutch) can be different from (as a rule less than) the thickness of the respective annular section.
The teeth can merge radially into the respective annular sections, namely in such a way that the cross sectional area of each tooth decreases in a direction away from (the internal or peripheral surface of) the respective annular section. Furthermore, the teeth can be configurated and dimensioned in such a way that each tooth includes a first portion which is affixed to (e.g., of one piece with) the respective annular section and a second portion which extends from the respective first portion substantially in a circumferential direction of the respective disc; the second portions of the teeth can be separated from the adjacent internal or external surfaces of the respective annular sections by narrow slots or gaps of constant width of varying width. The first portion each tooth can taper in a direction substantially radially of the axis of the clutch and away from the internal or external surface of the respective annular section.
As a rule, the dimensions of the teeth and of the splines are selected in such a way that the external surfaces or faces of the teeth exert pressure upon but are still slidable along the neighboring splines of the respective hubs; the clutch preferably further comprises means for reducing the pressure between the tooth faces of at least one set of teeth and the respective splines. Such pressure reducing means can comprise elastic films on the faces of at least some of the teeth. Alternatively, or in addition to the elastic films, the pressure reducing means can include the aforementioned second portions of the teeth constituting the aforementioned at least one set of teeth.
The teeth of at least one set of teeth can contain or consist of spring steel. Moreover, the at least one second clutch disc or each second clutch disc can comprise friction linings which frictionally engage the at least one first clutch disc or the neighboring one of two or more first clutch discs, at least when the clutch is at least partially engaged. The first clutch disc or discs can be devoid of friction linings.
The aforementioned at least one fluid-operated cylinder and piston unit of the means for biasing the clutch discs against each other in the at least partially engaged condition of the clutch can be designed to define a plenum chamber for a hydraulic fluid which is admitted into the chamber in order to at least partially engage the clutch, and the biasing means can further comprise a membrane which is disposed in the chamber between the supply of fluid and the reciprocable piston. It is presently preferred to employ an at least substantially annular membrane having a marginal portion which is maintained in sealing engagement with the cylinder of the cylinder and piston unit in a region between the piston and the supply of fluid in the plenum chamber.
The aforementioned marginal portion or each of the two marginal portions of the annular membrane can be provided with a bead or an analogous thickened zone which sealingly engages the cylinder, e.g., by extending (by snap action and/or otherwise) into an annular socket of the cylinder.
The membrane can be provided with at least one annular corrugation which is adjacent the piston, and such corrugation can be provided in the membrane before the latter is installed in the cylinder and piston unit.
The dimensioning and the manner of mounting the membrane in the cylinder and piston unit can be such that the properly installed membrane is movable in the axial direction of the disc clutch through a distance of up to about 5 mm (preferably of up to about 4 mm) in response to movement of the piston relative to the cylinder in a direction to pressurize the supply of fluid in the plenum chamber, i.e., to engage the disc clutch to a desired or required extent.
The entire membrane, or at least a substantial (such as major) portion of the membrane, can have a thickness of approximately 0.8 mm. The membrane can consist of an elastomeric material, such as fluorosilicone caoutchouc. Alternatively, the membrane can be made of a metallic material. If the membrane is made of or contains an elastomeric material, it can contain reinforcing means, for example, glass fibers and/or other filamentary reinforcing material.
The fluid in the plenum chamber of the cylinder and piston unit is being acted upon by centrifugal force and/or is otherwise influenced (when the disc clutch rotates) in a sense to undesirably affect the extent of engagement or disengagement of the clutch. In order to eliminate or lessen such influence(s), the disc clutch can further comprise means for counteracting any undesirable or non-controllable bias upon the piston, namely a bias which would or could affect the accuracy of engagement or disengagement of the clutch (i.e., which could cause the actual extent of engagement or disengagement of the clutch to deviate from the desired optimum extent).
The counteracting means can define a second chamber which is or can be provided in the cylinder and piston unit of the biasing means, and a supply of a fluid medium in the second chamber. Such fluid medium is being acted upon by centrifugal force when the two hubs rotate to thus bias the piston counter to the direction in which the piston is urged by the fluid in the plenum chamber (not as a result of admission of fluid into the plenum chamber but rather as a result of undesirable influences (such as by centrifugal force) upon the fluid in the plenum chamber). The supply of fluid medium in the second chamber can constitute a coolant for the clutch discs, and the clutch then further comprises means for directing the coolant into heat-exchanging contact with the discs.
The counteracting means can further include a piston member which is provided in the cylinder and piston unit adjacent the second chamber. The effective (fluid-contacting) surface of the piston member can match or approximate the effective surface of the piston which serves to vary the pressure of fluid in the plenum chamber. The piston member is acted upon by the fluid medium in the second chamber to oppose the bias upon the piston of the cylinder and piston unit when the hubs are caused to rotate.
The piston member of the aforementioned counteracting means can include or constitute a diaphragm spring which biases the piston of the cylinder and piston unit counter to the direction in which the piston is caused to move in order to urge the clutch discs against each other with an increasing force. The diaphragm spring can be designed in such a way that it includes a circumferentially complete annular portion and tongues or prongs extending from the annular portion at least substantiallly radially toward the axis of the disc clutch. The prongs define slots which are preferably filled by a suitable sealant. The sealant can coat at least a portion of at least one side of the diaphragm spring. Such sealant can contain an elastomeric material, e.g., fluorosilicone caoutchouc. It is often preferred to apply the sealant to one side of the diaphragm spring, at least in the region of the aforementioned tongues or prongs.
One or more sealing devices (e.g., in the form of washers or the like) can be provided to cooperate with the piston of the cylinder and piston unit and/or with the diaphragm spring (second piston) to at least partially seal the second chamber from the surrounding atmosphere.
Another feature of the invention resides in the provision of a disc clutch which comprises a first hub having external splines and being rotatable about a predetermined axis, a second rotary hub which spacedly surrounds and is coaxial with the first hub and has internal splines parallel to the axis and to the external splines, first friction generating means including at least one first annular clutch disc having a set of internal teeth which mate with the external splines of the first hub, second friction generating means including at least one second annular clutch disc having a set of external teeth mating with the internal splines of the second hub, and operating means which is actuatable to engage and disengage the clutch and includes means for biasing the first and second clutch discs against each other. The biasing means comprises at least one cylinder and piston unit including a movable piston and defining a plenum chamber for a supply of fluid (such as oil). The cylinder and piston unit further comprises a membrane which is disposed in the plenum chamber between the supply of fluid and the piston.
A further feature of the invention resides in the provision of a disc clutch which comprises a first hub having external splines and being rotatable about a predetermined axis, a second rotary hub spacedly surrounding and being coaxial with the first hub and having internal splines, first friction generating means including at least one first annular clutch disc having a set of internal teeth mating with the external splines of the first hub, second friction generating means including at least one second annular clutch disc having a set of external teeth mating with the internal splines of the second hub, and operating means which is actuatable to engage and disengage the clutch and includes means for biasing the discs against each other. The biasing means comprises at least one fluid-operated cylinder and piston unit having a plenum chamber for a supply of hydraulic fluid serving to (directly or indirectly) bear upon the reciprocable piston of the cylinder and piston unit and to thus shift the piston in the cylinder of the cylinder and piston unit in the direction of the predetermined axis to thus at least partially engage the clutch. The fluid in the plenum chamber is being acted upon by centrifugal force and/or is subjected to other influences, at least when the hubs rotate, to thus bias the piston in the aforementioned direction, and the improved disc clutch further comprises means for counteracting the (undesirable) bias upon the piston.
An additional feature of the invention resides in the provision of a disc clutch which comprises a first component including a first hub having external teeth and being rotatable about a predetermined axis and a second rotary hub spacedly surrounding and being coaxial with the first hub and having internal teeth (the just discussed teeth can constitute elongated axially parallel splines of the respective hubs), and a second component comprising first friction generating means including at least one first annular clutch disc having internal teeth mating with the external teeth of the first hub and second friction generating means including at least one second annular clutch disc having external teeth mating with the internal teeth of the second hub. The teeth of at least one of the first and second components (i.e., of the hubs and/or of the discs) are at least partially deformable (preferably elastically deformable), and the teeth of the clutch discs are movable relative to the teeth of the respective hubs. The disc clutch further comprises operating means which is actuatable to at least partially engage and disengage the clutch, and such operating means includes means for biasing the clutch discs against each other.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved disc clutch itself, however, both as to its construction and the modes of assembling and operating the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.